1. Field of the Invention
This invention relates to photographic objectives of the modified Gauss type, and more particularly to such objectives suited to be used as the standard lens for 35 mm single lens reflex cameras. In one form the objective includes four meniscus lenses and a fifth lens having positive power and a rear surface having a strong refractive power.
2. Description of the Prior Art
In general, the Gauss type objective is, because of its having a cemented lens just in the rear of the diaphragm, feasible to achieve good correction of chromatic aberrations such as longitudinal chromatic aberration, lateral chromatic aberration and color comatic aberration. On the other hand, an objective of what may be called the modified Gauss type with five elements constituting five components is disclosed, for example, in U.S. Pat. No. 2,720,139 and Japanese Pat. No. Sho 38-12983 where the first and second counting from the front are positive meniscus lenses of forward convexity, the third is a negative meniscus lens of forward convexity followed by a diaphragm, the fourth is a negative meniscus lens of rearward convexity, and the fifth is a positive meniscus lens. This type of objective is advantageous in minimizing the bulk and size of the apparatus. It is, however, very difficult to make the lens which follows the diaphragm, which is important to provide satisfactory correction of chromatic aberrations, since this lens is a singlet.
Therefore, this residual chromatic aberration must be compensated for by the suitable design of other lenses. It is, however, impossible in the present state of the art to achieve as good a correction as when the doublet is used in the rear of the diaphragm. Such substitution of the singlet for the doublet further aggravates other aberrations such as spherical aberration and curvature of field. As compared with the six-component Gauss type objective, there is a clear distinction in the optical performance. As a result, the general trend is to reduce the angular field, or the F-number to as dark a value as F2 or less in order to preserve the image quality.